Problem: Kevin is $4$ times as old as Daniel and is also $6$ years older than Daniel. How old is Daniel?
Explanation: We can use the given information to write down two equations that describe the ages of Kevin and Daniel. Let Kevin's current age be $k$ and Daniel's current age be $d$. Let Kevin's current age be $k$ and Daniel's current age be $d$. ${k = 4d}$ ${k = d + 6}$ Now we have two independent equations, and we can solve for our two unknowns. Since we are looking for $d$, and both of our equations have $k$ alone on one side, this is a convenient time to use elimination. Subtracting the second equation from the first equation, we get: $0 = {4d} -{(d + 6)}$ which combines the information about $d$ from both of our original equations. Solving for $d$, we get: $3 d = 6$. $d = 2$.